1. Field of the Invention
The present invention relates generally to a system for defibrillating a heart. More particularly, the invention relates to a system for defibrillating a heart using a transesophageal path. The invention also concerns such a system which, in the alternative, allows use of a transthoracic path for the defibrillating energy. The invention may provide for pacing the heart and/or ECG monitoring.
2. Prior Art
Sudden cardiac death from ventricular fibrillation is a leading cause of mortality. The most important factor in determining patient survival is early defibrillation. However, a significant percentage of patients with cardiac arrest present with refractory ventricular fibrillation. These patients may not respond to standard cardiopulmonary resuscitation, transthoracic shocks, or drug therapy. The clinician, therefore, must decide whether to continue or terminate the resuscitative effort.
The most common mechanisms for high defibrillation thresholds include elevated transthoracic resistance due to obesity or chronic obstructive pulmonary disease, prolonged duration of ventricular fibrillation, presence of ischemia or anaerobic metabolism, and superimposed drug therapy.
The success of a transthoracic shock is partially dependent upon the distance of the energy-applying electrodes from the heart, which is one determinate of transthoracic impedance. A more effective method of defibrillation would involve placement of defibrillator probes either into or in close proximity to the myocardium. Recently, intracardiac transcatheter defibrillation has provided a means of defibrillation for patients with refractory ventricular fibrillation induced in the electrophysiology laboratory. This technique is performed by defibrillating between a distal right ventricular pacing electrode and a posterior skin patch. The impedance between these two electrodes is less than the impedance between two electrodes located in standard positions on the thorax. This method, however, is performed most expeditiously if a temporary pacing lead is already present in the right ventricle.
In the past, transesophageal techniques have been employed primarily for atrial pacing and cardioversion of atrial arrhythmias. A braided copper esophageal electrode (15 cm in length; 9 mm in diameter) has been tested in conjunction with a maliable lead precordial electrode and was capable of terminating ventricular fibrillation in canines using high energy defibrillation, as reported in Whipple G. H. et al., "Transesophageal Ventricular Defibrillation" (abstr.), Clin Res 1956; 4:105. The effect of cardioverting using a Levine tube wound with copper wire is known and has been reported in McNally E. M. et al., "Elective Countershock In Unanesthetized Patients With Use Of An Esophageal Electrode", Circulation 1966; 33:124-127. This was accomplished by delivering direct current energy between the esophageal electrode to a precordial patch in 13 patients with atrial fibrillation. More recently, it has become known that a French hexapolar esophageal probe in canines was used to successfully terminate ventricular tachycardia and fibrillation; see Yunchang C. et al., "Transesophageal Low-Energy Cardioversion In An Animal Model of Life-Threatening Tachyarrhythmias", Circulation 1989; 80:1354-1359. These arrhythmias were terminated immediately and thus did not assess the potential for rescue defibrillation of refractory ventricular fibrillation. However it is unlikely that these prior art techniques would be effective in cardiac arrest patients in light of the small electrode surface area as well as the low energies employed.
It has been recognized that when a person's heart is beating at a slow or an irregular rate, or after defibrillation, the heart should be stabilized to beat at a particular rate. An electronic pacing method and apparatus is known from U.S. Pat. No. 4,574,807 which can achieve such pacing without surgery using a flexible tube or rod having a series of circumferential electrically conductive rings spaced a few centimeters apart and electrically connected together which may be inserted down the esophagus so as to place the rings in the lower portion thereof. A second electrode, which may be a conventional adhesively attached ECG electrode, is attached to the sternum. An electrical pacing pulse of short duration and low power is passed between the electrodes. The pulses stimulate the heart muscles and make the heart beat at a preset rate. The tube or rod carrying the electrically-connected-together rings may be small enough to pass through an esophageal gastric tube or similar device. No provision is made for supplying defibrillating energy.
A somewhat more complex system for pacing the heart from the interior of the esophagus, is disclosed in U.S. Pat. No. 4,640,298 which discloses a probe constructed on the basis of a finding that the distance from the transition between the stomach and the esophagus to the transition between the left atrium and the left ventricle is substantially the same in adults. The electrode probe has a maximum of two stimulation zones (one for atrium and ventricle, respectively) which, when fitted on expansible parts of the probe, allows heart pacing to be performed with simple equipment without expert assistance, when the distance between a means for fixing the axial position of the probe in the esophagus and the stimulation zones are determined in accordance with the finding. Good stimulation of the heart and reduction in the required pacing voltages are achieved. No provision is made for supplying defibrillating energy.
A non-invasive cardiac device is disclosed in U.S. Pat. No. 4,706,688 which can be inserted through the esophagus and into the gastroesophageal junction region. Once in place, a selected portion of the device is urged adjacent the cardiac region. The device includes an elongated conduit having a series of spaced-apart ring electrodes for sensing or recording electrical signals. A first inflatable cuff is provided for positioning the device adjacent the gastroesophageal region is located adjacent a first end of the device. The device further includes a second inflatable cuff for positioning the device in the esophagus such that at least some of the ring electrodes carried by the conduit are urged adjacent the cardiac region. The spaced-apart electrodes are used in pairs to pass electrical signals to the heart for atrial/ventricular pacing and to receive electrical signals from the heart for electrogram analysis. It is proposed to supply low current defibrillating energy to the heart, apparently via a pair of the ring electrodes carried by the conduit. Neither an anterior patch nor a posterior patch is provided for any purpose.
A method and apparatus are disclosed in U.S. Pat. No. 4,735,206 to provide defibrillating energy to a heart using a small internal esophageal electrode and an external small chest electrode. The two small intimately located electrodes, one in the lower esophagus where it is intimate to the posterior section of the heart and the other small electrode on the chest over the sternum where it is close to the anterior portion of the heart, provide an electrical path between the two electrodes. An electrical pulse having a peak of approximately 150 volts is delivered. During this period, gentle repolarizing of the heart takes place. When the heart is repolarized, the heart cells become neutral. They are vulnerable to a stimulus. The defibrillation pulse may be immediately followed by a stimulus in the form of pacing pulses that are at the rate of approximately 70 to 100 pulses per minute and of a magnitude of approximately 75 to 150 milliamps. The switch from one mode to the other is made without changing the location of the electrodes. No provision is made for providing a plurality of electrically separated electrodes within the esophagus nor a large area patch on the chest.
A method and apparatus for achieving atrial defibrillation or ventricular defibrillation using a small single, internal esophageal electrode and a single moveable small external chest electrode is disclosed in U.S. Pat. No. 5,052,390. Atrial defibrillation is attempted using the internal esophageal electrode and with the small external chest electrode placed approximately on a line between the two nipples and part way between the sternum and the left nipple. This provides a good path for the defibrillating pulse so that defibrillation is said to be accomplished with very low power of 30 to 70 joules (average 50 joules) compared to what is normally used, namely, 100 to 360 joules. Ventricular defibrillation is said to be possible using the small internal esophageal electrode and an external chest electrode placed approximately over the apex of the left ventricle. This provides a good path for the defibrillating pulse so that the power needed, it is said, may be of the same magnitude as that used for atrial defibrillation for the purpose of ventricular defibrillation. No provision is made for providing a plurality of electrodes within the esophagus nor a large area patch on the chest.